Such a method is known from GABOR, M. and NEREM, S., Satellite-satellite single difference phase calibration as applied to ambiguity resolution, Navigation, Vol. 49, Nr. 4, pp. 223-242, 2002 [2]. The known method uses the ionosphere-free Melbourne-Wübbena (=MW) combination [1]. In a reference station a satellite-satellite single difference (=SD) phase and code bias is estimated, wherein the estimated bias is provided to a mobile receiver, which computes the same linear combination, substracts the bias from the linear combination and determines integer phase ambiguities.
The MW combination is widely used for precise point positioning (=PPP) to determine the widelane ambiguities. The MW combination is a geometry-free L1/L2 code-carrier combination that removes the tropospheric delay, the clock offset and further non-dispersive error sources. The MW combination and an additional ionosphere-free L1/L2 phase combination are used in particular in [2], [3] and [4] to determine L1 phase bias estimates.
However, there exist a variety of disadvantages of this known method: First, the L1 and L2 phase biases can not be separated from the L1 and L2 code biases, i.e. the L1 phase bias estimate also includes weighted L1 and L2 code biases. Secondly, the Melbourne-Wübbena combination refers to a geometry-free, ionosphere-free linear combination which eliminates the range and can not be used for positioning. In principle, geometry-preserving, ionosphere-free combinations can be found where the L1 and L2 bias of the known method are applicable, but these combinations are narrowlane combinations with a wavelength of at most 10.7 cm. This rather low wavelength prevents any reliable ambiguity resolution at the mobile receiver.